Remote supervisory radio signaling system



Dec. 11`, 1951 w. s HALSTEAD REMOTE sUPERvIsoRy RADIO SIGNALING SYSTEM 8 Sheets-Sheet l Original Filed April l2, 1941 INVENTOR ATTORNEY Dec. 11, 1951 w. s. HALSTEAD REMOTE sUPEEvIsoRY RADIO SIGNALING SYSTEM 8 Sheets-Sheet 2 Oiignal Filed April l2, 1941 @hulk bwk INVENTOR ATTORNEY Dec. 11, 1951 w. s. HALsTl-:AD 2,577,751

REMOTE SUPERVISORY RADIO SIGNALING SYSTEM Original Filed April l2, 1941 8 Sheebs-Sheet 3 Q Eg Q fsw@ a b:

ECE/VE ANZ CONNECT/ON To F/LAME/vrs ATTORNEY.

Dec. 11, 1951 w. s. HALSTEAD 2,577,751

REMOTE SUPERVISORY RADIO SIGNALING SYSTEM Original FiledApril 12, 1941 8 Sheets-Shea?l 4 h n. I .QQ

INVENTOR.

/ ATTORNEY.

Dec. 11, 1951 w. s. HALSTEAD 2,577,751

REMOTE SUPERVISORY RADIO SIGNALING SYSTEM Original Filed April l2, 1941 8 Sheets-Sheet 5 FIG. 6.

Dec. 11, 1951 W. s. HALSTEAD 2,577,751

REMOTE SUPERVISORY RADIO SIGNALING SYSTEM Original Filed April l2, 1941 8 Sheets-SheefI 6 FIGURE@ /1// /AM 5T ,f7/,4457540 INVENTOR.

ATTORNEY Dec. 11, 1951 w. s. HALsTEAD REMOTE SUPERVISORY RADIO SIGNALING SYSTEM 8 sheeisheet 7 Original Filed April l2, 1941 ATTORNEY Dec. 11, 1951 wjs. HALSTEAD 2,577,751

REMOTE suPERvIsoRY RADIO SIGNALING SYSTEM Original Filed April l2, 1941 8 Sheets-Sheet 8 ATTORNEY PatentedDec. 11, 1951 :anni

mING

SYSTEM William S. Halstead, Purchase, N. Y., assignor, by mesne assignments, to Farnsworth `Research Corporation, a corporation of Indiana Original application April 12, 1941, Serial N0. 388,338, now Patent No. 2,459,105,1lated January 11, 1949. lDivided and-this applicationv March 24, 1945,v Serial No. 584,589

3 claims.' (C1. 25o-6) This invention pertains to traflic signalling, and in particular relates to a traic control and communications system of the general type as disclosedin the Halstead patent Reissue No. 21,818. This is a division of application for U. S. Letters Patent, Serial No. 388,338, led April 12, 1941 and which issued as U. S. Patent No. 2,459,105 on January ll, 1949.

The system of the Halstead patent involves the use of electric carrier Wave energy for commu? nicating intelligence vtotraflic within predetermined signallng zones by means of speech signals and audio frequency control signals which serve to selectively actuate visual indicators, such as stop, go, or caution signal lights. The audio frequency control signals mayalso so be rendered audible, to serve as an aural check, by means of the same electro-acoustic apparatus that is employed for reproduction of the speech signals.

The presentyapplication incorporates certain of the principles disclosedin the original system and includes improvements and modications for effecting two-way auralv communications aswell as protective visual and aural signalling, for the purpose of attaining positive, centralized control of traic operations within a given signalling zone.

In applying the system of the Halstead-patent to speciiic traiiic signalling fields, antexample. ofv

which may be that of classification yard signalling, certain modications and improvements have been found to be desirable .in order to more effectively adapt theoriginal system to the conev ditions peculiar to the particular service. For example, it has been determined that two-*Way aural communications between a central point and operators of vehicles, such as locomotives, or motor trucks, within-a terminal area is desirable, and that constant periodic transmission of a protective aural and visual checking signal at predetermined intervals isy of particular value in preventing damage to equipment or operating personnel in the event of failur'e of the control station transmitter or vehicle receiving equipment. Also, it has been found desirable to provide an automatic control meansoperable by Wave energy transmitted from a remote transmitter, Which may be on a vehicle, whereby the control station transmitter is locked-out of operation while signals are being received from the remote transmitter. n

Although the system of the present invention is particularly applicable t0 signalling in large terminal areas, such asclassication yards, the embodiment of the inventionf `as described herein is illustrative only, and represents a specic example ofthe application of the system of theV invention tofreight classication service. This application,therefore, does not constitute a limitation since the exibility of the system issuchthat itA may be used in signalling zones along rail--A waygmain lines, in various terminal areas, or in other vehicle communications and. traiiic signalling services.

The present embodiment of the invention emr-f braces a coordinated aural-visual communications and 4signalling system constantly under supervisory control of automatic protective, or

fcheckingf signal circuits. Carrier wave energy,` modulated byvoice and control signals, is transmitted from a control station to vehicles Within a given signalling zone. Receiving equipment on all vehicles Within the zone, may, ifk desired, be

tuned to respondto carrier Wave energy, of a predeterminedy zone frequency, which is transmitted, from the control station. Thus, the operator .of 'the control station may be the central coordinator of all movements of vehicles,.such as locomotives, within the signalling zone. This zone,`

in the case of classication yard signalling, may extend'from vthe. transmitter in every direction throughout a yard area, or it may be localized,`

along specificlanes of traiic by directional waveenergy transmitting systems as disclosed in the Halstead patent.; I

In order to more completely ensure eflicient and safe operation oivehicles within the signalling area, automatically,transmitted periodic checking signal indicationsv are provided in both the control station and in vehicles. This permits continuous supervision ofA operation of control transmitter equipment and receiving units in all vehicles as will be described in further detail.

It is essential in-any traic signalling and communication systemin which orders of any nature are periodically. transmitted to moving ve-v hicles to rprovideY a means for the prevention of accidents which might result from failure ofthe transmission and reception equipment. Suppose,`

for example, that a control dispatcherhas given auralfproceed instructions to the engineer 'of afpusher locomotive located at the rear of a long freight train 'proceeding toward the hump` of al classiiication yard. Under these conditions,

particularlyif wayside signals are obscured by a fog or storm, the engineer will continue to move the locomotive until another signal is received to caution him or, to direct him to cease the move'- ment. Should the control transmitter or locomotiiefeeivieg'appar-aimerait the 'engineer would assume that he should continue to move even though, in the meantime, the control operator has issued instructions to stop. It is obvious that the dispatchers instructions wouldhbe ineffective in bringing the locomotive to a stop, not being aware of failure of equipment. Under this condition a serious accident might result.

Thus, in order that the engineer lmay ascertain at all times that the central station transmitter and locomotive receiver are in proper Working order, an over-all protective checking system of automatic type is incorporated in the novel con# trol means of the present invention. This checking system operates, in a general sense, upon the closed circuit principle in that failure of any part of the signalling system will automatically be indicated. A

The checking system comprises a continuously operative means for transmitting a periodic control signal of a particular form which may be received by the engineer to indicate that he is receiving signals from a central station.

In the illustrative embodiment of the inven-l tion described herein, the control station emits a `carrier frequency, modulated by a particular audio frequency which is transmitted periodi cally to the engineer. This signal is preferably in the form of a periodic series of impulses which may be manifest in the engineers cab. by aural or visual means.

This periodic carrier signal modulated by voice signals or by a particular control frequency may be employed at the mobile receiver to energize a sound reproducer or to selectively energize a; particularchecking or proceed indicator lamp in order that the engineer may know that. he is in contact with the controlY station and may proceed in safety with a given order.v During the transmission of speech from the central station, itis desirable that the checking system cease to operate in order that an uninterrupted intelligiblev voice signal may be received'. To effect this function, the present invention employs a selective control circuit which automaticallydispenses with the checking or proceed signals when the central transmitter operating switch is closed.

When the engineer desires to acknowledge the receipt of a particular control signal, he Vmay,

by means of his transmitter, send back a signal to the control station. This may be accomplished by voice signalling from the mobile unit, or by the simple closure of the transmitting switch in accordance with a predetermined code',.which',

when received at the control station, will automatically cause the visual operation of a carrieractuated signal light.

In order toprevent interference with reception of a voice signal from a locomotive transmitter byl the periodic actuation of the central control transmitter, a novel, carrier-actuated lock-out circuit is employed to automatically preclude op-V eration of` the central station transmitting op` eration and to keep the central station receiver in its normally-on `condition while a carrier sig-Y nal is being received. This lock-out circuit also serves to prevent manual operationrof Vthe central transmitter as long as a carrier wave from a locomotive transmitter is being received. A visual indication of reception of a carrier wave from a locomotive transmitteris also provided for` supervisory or acknowledgment purposes.

Thus, by V,means of automatic controls and visual signal indicators, a coordinated signalling system of highly dependable nature iS Provided.

4 The possibility of simultaneous operation of both central station and mobile transmitter is also removed.

It is an object of this invention to provide a novel traic signalling system for transmitting speech and protective control signals to traffic Within a signalling zone.

It is an additional object of this invention to provide a novel two-Way tramo communicating system for transmission and reception of visual and aural controlV signals within a signalling 1 zone.

It is a further object of this invention to provide means wherebya control signal from a first electric wave transmitter Will lock-out and prev e'nt operation of a second remote transmitter whilersaird rst transmitter is emitting its lockout control signal. l

It is another object of this invention to provide means whereby a periodic control signal is :automatically emitted at predetermined inter vals from a signal transmitter at one station to a cooperating receiver at a second remote station to serve as a checking, or supervisory, signal for indicating that said transmitter and said receiver are operative.

Another object of this invention is to provide a trahie communications and control system for coordinatingV the movements of vehicles in a traffic area which is effective to automatically indicate failures in the transmission and reception system.

Another object of the invention is to provide for 'a comprehensive tramo control system for a railroad freight classification yardk or similar terminal area wherein each of the locomotives or other vehicles is adapted to receive and transmit. control signals, each relating to a particular freight yard operation.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawings and its scope vwill be pointed out in the appended claims.

Referring to the drawings:

Figure l is a block diagram of the transmitting and receiving equipment employed at a central control station disposed adjacent a traic signalling zone.

Figure 2 is a block diagram of transmitting and receiving equipment employed in a locomotive or other vehicle operating within the signalling zone of the central control station.

Figure 3 is a circuit diagram of transmitting equipment employed at the central control station.

Figure 4 is a circuit diagram of a present-employed receiver utilized at the central control station.

Figure 5 is a front elevational-view of one preferred arrangement cf a microphone, signal lights, and a loudspeaker disposed at the central control station. y

Figure 6 is a side elevational view of the apparatus shown in Figure 5.

Figure 7 is a circuit diagram of a present-employed transmitter and receiver installed on a locomotive within the signalling zone of the central control station.

VFigure 8 is acircuit diagram of a two-channel audio-frequency filter and checking-signal control relay and loudspeaker circuit employed in the present embodiment of the* invention.

Figure 9 is a front elevational view of a presnal lights, and flexible supportingarm employed inthe locomotive. .y M l Figure r1o is a .from eleyationalfviw uof me microphone and signal light unit of VvFigure 9 .with

thefront coverremoved-- l Figure 11k is a side elevational view of the mi'-4v crophone and signal light arrangement,.showingH the disposition of a shock-mounted .microphone and signal lights .within-a housing such as illuse. trated in Figure 9.

Figure 12 illustrates a position .of voice and protective'signalling equipment of the system Within a locomotive cab. Referring now more particularlytoA Figure 1,. there is shown a schematic representation of the. central control station transmitter and receiver.; 'IP-his figure is merely a .diagrammatic representa'. tionvof the more detailed circuit diagrams shown. inV Figures 3 and 4 and the following description. of the component parts'will correspondfor all of theseflgures.

v-The lcentral control station may be located in the most accessible point of the limited area over which coordinating signals aretobe transmitted. Thus, if the system to lbe described israpplied to a -freight classification yard, the central.. station may be disposed most conveniently adjacentthe hump. The transmitter: and receiver at .the .hump may be remotely controlled from one .ormore points if desired. A

From these control points, the humpfconducf tor, yard master or other control station .operatormay be in a position to best. determine the.

nature of the signal to be transmittedto loco.-l

motives equipped with coacting signalling apparatus, which may be of the form diagrammatif cally illustrated in Figure 2 and more particularly in the circuit diagrams of Figures 7 and8. Essentially, the central station includes a combined transmitter and receiverfor establishing two-way voice communciations ..and autor.. matic protective signalling withv locomotives or. other vehicles operating .within a4 given .signalling zone, such as the classification yard .area As ris illustrated in thev embodiment ofthe in. vention shown in Figure l, a receiver.2| and a.

ltransmitter 22 utilize a single antenna 23 which is joined to the transmitter ,or receiver throughv an antenna transfer relay 24. The .receiver 2| may .comprise conventional ,equipment for .demodulating and amplifying a modulated signal radiated from the antenna .whichis energized by aftransmitter 52 (Figure 2) y,disposed upona locomotive or a similar vehicle.; The v,signal radiated from antenna 5| is interceptedby,antenna 23 at the central stationandV applied to the receiver 2| (Figure l) which in turna-pplies the demodulated signal energy to a loudspeaker- 25 for rendering the received signals audible.vvv

The transmitter 22 at the controlstation may also .comprise conventional vequipment forgam'- plifying electrical signals. impressed .upon thcinput circuitsthereofand. causing these signalsvkto modulate a radio frequencycarrierwhich is thenY radiated into .space through antenna 23for re: ception by antenna 5| of Figure 2 and; itsbcoacting receiver 53 disposed upon a movablevhcle. The signals applied to the input of transmitter 22 may comprise voice currents generatedinY niicrophone 26 or a constant-amplitude audio fre,- quency control signal generatedat source 21 for utilization .by protective checking 4apparatus ,at the. central station` illustrated. in Figure 1 and corresponding apparatus .atthe moyable .Station present-preferred.v dis-Y comprise batteries or alternating current.

these circuits.

This audio frequency control signal is'coupled,

to the transmitter through a transfer relay 3| whichis manually controllable by a suitable switch such as the foot switch 32. Undernormal conditions, the transferrelay 3| is in a position, where the audio frequency energy from signall source 2l may be applied to the input of the transmitter 22.` The antenna transferrelay 2li is nor,-

mally in a position for applying the signals inter-.,

cepted by antenna 23 to the receiver 2|.

The receiver 2| and transmitter. 22 are enerr.' gized from any available power source which may. The.

iaments of the various vacuum tubes utilized in.

these circuits are continuously energized whereas: the plate circuits of the transmitter and receiver.

are selectively energized from a high voltage source connected with either the transmitter or y the receiver through the power transfer relay 33..

The movable members of the power transfer relay operate simultaneously with the movable members of the antenna transfer relay 24. Thus when the antenna 23 is coupled to the receiver 2 I, the power transfer relay applies the high voltage to the plates of the receiving tubes. Conversely,

when the antenna transfer relay interconnects the antenna 23 and the transmitter 22, the power transfer relay serves to permit the energization of the transmitter vacuum tubes and to deenergizethe plate circuits of the receiver 2 I.

An automatic keying device 3d is continuously operated and under normal operating conditions determines the movement of the power transfer relay 33 and the antenna transfer relay 24, and

effects periodicoperation of the relays. The key-v quency carrier modulated by the constant-ampli-` tude audio frequency control signal provided by the control signal source 21. This energizing volt age is of relatively short duration and thus the radiated checking signalv is in the form` vof'a' plurality of periodic modulated impulses. 1 During the normal non-keying portion of the operating cycle of the keying device 34, the power' normally-on condition to accept incoming signals from a transmitter of the type indicated in Figure 2, and to impress them upon loud speaker'25.

Accordingly, the central station during its oper? ation transmits a series of periodic impulses and is in a position for receiving signals in the'intervening time. If the operator of the central controlv station desires to transmit instructions to the vehicle carrying the apparatus illustrated in* Figure 2, operating' Within the 'localized areas such as the freight classification yard,lthe switch' 32 is depressed which in turn causes the operation of transfer relay 3|. Af

As previously described, the transfer relay,' 3'|, when energized disconnects the modulating con-- trol signal source 2'! from the input circuit of the transmitter and couples the microphone thereto. In addition, the operation of transfer relay energizes power transfer relay 33 and antenna transfer relay lo .apply venger in? Preis:

mitterplate eireuits,-and.to coupie the antenna 23 tothetransmitter output circuits.

Thus, it may be seen that speechfsignals applied Ato the microphone 23 will .be caused to modulate the output circuits of transmitter and. amodulated signal will be radiated from antenna 23. The central station circuits will be in a condition for transmitting speech signals as long as the switch 32 is closed.

When the desired instructions have been given by the control operator, the release of switch 32 will then automatically disconnect the microphone and apply the control signal generated within source 21 to the input circuits of the transmitter and thekeying device 34 will again resume control of the sequential application Aof power to the plate circuits of the receiver and transmitter and the corresponding application of the antenna 23.

The central control station'is provided with a plurality of pilot lights which indicate proper operation of the entire two-way communication system. These pilot lights are disposed in the operators eld of vision to facilitate checking operations. A pilot light 35 is provided to indicate the fact that a' modulated carrier is being radiated from antenna 23 during the operation of the transmitter. This is accomplished by a circuit which is inductively coupled tothe transmitter antenna circuit.

As will be hereinafter explained, the signal induced in this circuit is applied to a demodulating and audio-frequency signal rectifying circuit 3B which causes the operation of a relay 3l when a modulated signal is being radiated. The relay 3,1 vin turn energizes the transmitting monitor vsignal light 35. It is evident that during thc normal operating cycle, the monitor light 35 will be energized periodically by the modulated carrier which is caused to be periodically transmitted by the keyer 34.

An additional visual indication for the operator of the central station is a transmitting indicator light 4| which is energized whenever the power transfer relay energizes the plate circuits of the transmitter 22. Accordingly, during the normal operation of the control station, the monitor indicating light 35 and the transmitting pilot light 4| will be energized in unison.

On the other hand, when the foot-switch 32 is operated for the transmission of speech, the transmitting indicating light 4| will be continuously energized to indicate the application of power whereas the monitor light 35 will flash in accordance with the impressed signal voltage during speech transmission or other modulation.

When antenna 23 is energized by signals from a vehicle operating within the classification yard or other such area, the receiver 2| operates to demodulate these signals and impress the demodulated energy upon loud speaker 25.

To Vprevent interference with an incoming si.,-

nal from a locomotive transmitter by theautomatic or manual operation of the `central transmitter, a novel carrier-operated transmitter lockout control circuit is provided which automatically causes the periodic keying circuit v34 and input-transfer relay 3| to lose control over the operation of the power transfer relay 23 and the antenna transfer relay 273. This lock-out condition Will exist as long as a carrier-Wave from a locomotive transmitter is being received at the central station.

To effect this control function a carrier-controlled lockout relay 42 isprovided in. the audio amplifying and'fnoise suppression circuit ofthe receiver 2| and operates Whenever a carrierjs received by antenna 23 from a transmitter such as 52 indicated in Figure 2. ThisY relay when energized automatically disconnects the keying Vdevice 34 and transfer relay 3| and thuspermits meanswhereby signals from a vehicle may be4 received aurally Athrough the agency of loud speaker 25 or visually by pilot light 43. Thus, since the lock-out relay is operatedby an incoming carrier wave transmitted from the vehicle transmitter 52 illustrated in Figure 2, the operator of the .vehicle may, by momentarily keying his transmitter 52 through the agency of a switch 54, transmit an intermittent carrier which-Will energize pilot light 43 in accordance Iwith any 'predetermined signalling code of simple form.

Thus the engineer may acknowledge receipt of an instruction, or convey othery signal intelligence if it is not convenient for him to speak into lhis microphone.

Therefore. it may be seen that if the central station is arranged with the various circuit elements diagrammatically illustrated in .Figure l, it will continuously and automatically tran-smit a series of checking or control impulses .andbe in a position to receive signals inthe 'time between impulses.V

Furthermore, the central Station operator may transmit any desired speech signals and may receive incoming signals aurally or visually. Thus the central'station is equipped for two-way communication With a remotely disposed station such as that indicated'in Figure 2. If vthis equipment is applied to a railroad freight classification yard, then the radio apparatus of Figure 2 may be most conveniently located within the cab of a locomotive or upon Athe tender thereof. Essentially, the mobile equipment comprises the transmitter 52 and receiver 53, each cooperable with the 'single antenna 5| through a'relay 55 which selectively connects the antenna and the receiver orl transmitter.

Normally, the transfer relay 55-is in aposition where antenna 5| is coupledto receiver53 so that signals radiated from antenna 23 at the controlstation will be applied to the receiving equipment at the locomotive. The received signals aiteribeing demodulated in receiver circuits 53 are applied to a two-channel filter 56 which may, as will hereinafter be pointed out, comprise a parallel combination of high and low pass electric Wave filters.

The iilter`53 selectively applies received speech signals to a loudspeaker 51 for rendering such. speech audible to the locomotive engineer. Furthermore, this filter 56 separates speech signals' Therefore this checking light will flash in accordance with the received Vaudio frequency impulse in a mannersimilar to the monitor pilot light at the control station. Accordingly, the checking light 53 disposed preferably within the field of vision will provide a Visual indication by its flash that the central control station illustrated in Figure-1 and the locomotive receiving apparatusvare in properworking order.

As a further assurance of this fact, a portion of the checking signal energy may be allowedl to .pass through the filter 56 to the loud speaker 51 to render the checking signal audible as a tone of characteristic pitch andthus provide a combination of periodic visual and audible signals Within the locomotive for indicatingproper operation of the equipment. Y

As has previously been described in connection with Figure l, when the central station operator desires to transmit speech signals and depresses foot vswitch 52 the checking signals will -cease for the duration of the speech transmission, Thus the checking signal will not in- `terfere with the received speech transmissions. These speech transmissions will automatically be applied through the two-channel lter without appreciable e attenuation` to the loud speaker whenever. they are transmitted from the control station. s.

The transmitter 52 when operated, ensures positive coordination between the control station ,operator and the. locomotive engineer.

IThus, the transmitter 52 permits the engineer of the locomotive to acknowledge the receipt of v any specific instruction or to question any forder and to ask for instructions `whenever in doubt. The transmitter 52 .alsopermits an engineer of one locomotiveltocornmunicate with ,circuits 52.

e AIn addition,v the actuation of switch 54 will energize a power transfer relay 54 which operates in a manner similar to that ofV power transfer relay 33 which is disposed at the central controlstation. f

Accordingly, when the transmitter switch 54 ;is actuated, the power .transfer relay 64 disconnects the power source at the locomotive from the receiver and Aconnects the transmitter to this source. Hence the locomotive engineer may by speaking into microphone 65 call the operator of the central station at any time.

If, as previously mentioned, the locomotive engineer prefers to transmit a series of intermittent signals corresponding with a predetermined signalling code, he may by intermittently actuating the transmitting switch 54 key the transmitter to transmit a plurality of signalswhichv will be made evident at the control station by the intermittent flashing of lamp 43.

The power transfer relay serves in addition'to v, transfer the energy from the receiver circuit to the transmitting circuit to energize a transmitting pilot lamp 66 to provide visual indication e forvthe engineer that his transmitter is in op- .e eration.

This,k transmitter pilot iight may also te vdisposed inthe engineers iield of vision. As shown in oney modiication, the transmitting pilot 66 and the checking indicating light may be disl-n posed upon the engineers microphone 55 which in turn is always disposed in his field of vision as will be described in connection with Figure 12.

Thus, from the block-diagram. representation of a control station and a coacting transmitting and receiving unit which may be disposed upon a movable vehicle it may be seen that two-way voice communication may be established therebetween and that the operators of each stationl at all times have the additional protection afforded bythe positive, selective acy tion of visual indicators to show that the system is in proper workingorder.

To supplement the visualchecking signal, th locomotive operator, as pointed. out, also has an aural indicationl of reception of the checking signal. In the event of failure of any vportion of the central station ormobile equipment, such failure will `be visiblyv indicated. at the central station and also on the locomotive throughlack of visual or aural indication by the periodic checking signal. y

Under these circumstances, the locomotive engineer and/or the control station operator will immediately investigate and will immediately ycease all operations dependent upon the signalling system until .the fault has been corrected. V An embodiment of the traffic communication system schematically illustrated in Figures l and 2, particularly for adaptation to a classification yard or similar localized trafic area is more completely illustrated in Figures 3 through 12, and referencel is now made thereto.

In Figure 3, there is shown a circuit'diagram of one section of the control station schematically illustrated in Figure 1. The transmitter, vas indicated, is energized from an alternating .current supply impressed upon the terminals 1l. This alternating, current vis vthen rectified and applied to the transmitting circuits.

However, it is pointed out that any available power supply maybe utilized and may be converted to the. desired voltages in a manner which is well knownin the art.y V The alternating current impressed `upon terminals 'Il is impressed 'upon aV rectifier 12 through a power transformer i3, the high voltage secondary of which is joined to the anodes of the rectifier 12 in conventional manner. e e A A filament transformer 'i4 energizes the filament circuits of the Various vacuum tubes and a pilot light 15 affords a visual indication of the application of this voltage. f y

Another secondary winding 16 is utilized to energize the heater of rectifier l2. The center tap thereof is the positive terminal of the direct current supply for the anodes of the transmitter. A filter Ti issemployed to eliminate any ripple in the direct current supply.A The alternating current impressed .upony terminals 'H in addition serves to continuously drive a relatively small synchronous yor other substantially constant-speed motor 8l rwhich in turn drives a `cam 82.

This cam, havinga plurality of projections 83,

operatesr to periodically close the switch 84 to The constant frequency, output of the. osci1.

lil later R is applied to the'control eridof a power ampli-iler 9". I The anode ofthis amnliier is energizefi from the hiofh direct voltage source tbrnrgh a tank, coil-93 and through a radio frequency choke coil 94.

The output of the power amplifier is in turn coupled to the antenna .23 through coupling condenser SI5 and through antenna transfer relay 96.; When the transmitter of Figure 3 is in the normal` ooeratiner condition as illustrated. the closure of switch 84 under the iniiuence of cam 82 will. as illustrated. energize the coil 9'! of the antenna transfer relay 9S to couple the antenna-23 to the output circuitv of the amplifier 92, and so permit tbe radiation of the signal generated at the transmitter.

' Enercization of the relay coils is secured throuffh a small rectfying unit IUI which is preferably of the dry-disc type energized through transformer H32 from the main alternating cur-` rent supply.

As illustrated, an audio frecuency control signal is impressed upon the input circuit of -the transmitter. This signal, which functions vas the checking signal. described in connection with Figures l and 2, is preferably of a relatively low frequency alternating current and is thus most conveniently obtained by utilizing a harmonic of the alternating current power supply. y

Thus, as shown in Figure 3, the audio frequency control signal is obtained from the inout to the lter TI. A tap on variable resistor |533 is coupled through condenser m4 and through the switch members of the input transfer relay 3l to the primary of the input transformer IUE. The secondary of the transmitter input transformer |05 is coupled to the grid of a tube IDS, the. anodes of which are energized from the high voltage source through the primary of acoupling transformer IU'I.

The terminals of the secondary of transformer IEJ'I are coupled to the grids of a push-pull modulatortube III. The anodes of the tube II! are joined to the terminals -of the primary of a modulation transformerV I I2, the center tap of which is energizedfrom the high voltage source.

In the modulating circuit, as indicated'in Figure 3, the anode of the power amplifier S2 is coupled to the screen grid thereof through the tank coil^93 and the radio frequency choke 93. This parallel combination of screen grid and anode are then joined to the high voltage source through the secondary of transformer I I2. Thus the signals impressed upon the input transformer |05 cause corresponding fluctuations in the plate and screen grid circuitsrof the power amplifier 92. The modulated carrier, as previously described, is coupled throughv condenser 95 to the antenna 23. y

As hereinabove set forth, when relay 3| is in the normal position, jthe transmitter input ampliiier IQIB isin a condition to beenergisedfby the audio frequency energy tapped from powersupply resistor ID3 and passed through condenser IIM, and the switching members of transfer relay 3l. Thus, when power relay 33 is energized and power is. applied to the transmitter, modulating signal energy is applied Lto -the transmitter.

The audio frequency energy has a fundamen- `talof twice the alternatingfcurrent input frequencyv and thus mayibe. of thenrder .of A120 cycles ifa.commercial power line-.is .usedfor `a power supply at the terminals 'II;

When the various relays y:are in their Anormal i positionas illustrated` inFigure v3; it may be `seen 1,-2 that the switching members of power-transfer relay preclude the ow of current in the primaryof the plate transformer 13.

Accordingly. this precludes tbe energization of all the anode circuits ofthe transmittersince no voltaffe is impressed upon the anodes of the rectifier '52.

It is to be noted, however. that the transmitter is normally kept in a condition where tbe imneediate energization thereof may be eiiected. Thus the primary of the filament transformer 'Iii is continuously energized from the power impressed upon terminals 1I. The plate transformer 'I3 is dependent upon Vthe position of the switching rrembers of the power transfer relay 33 for energzation.

During the rotation of motor 8|, the cam projection 83 will close switch 84 and as may be seen from the circuit diagram, will thereby This will simultaneously cause the application of a high direct-current potential to the anode of the Various vacuum tube circuits illustrated and supply the low frequency signal-to the primary of input transformer I 05.

' The coil 91 of the antenna transfer relay 2d is in parallel with the operatingl coil of power transfer relay 33 and consequently when the switch Sd is closed by the ,cam 82, the antenna transfer relay will operate to cause the arm 24 to move downwardly as viewed Vin Figure 3 and connect the antenna 23 to the tank coil 93 through coupling condenser 95. Y

Therefore, the carrier modulated by a conetant-amplitude audio frequency control signal is radiated into space when switch 84is closed. Since the filaments of the various electron tubes are normally, heated in this power transfer system, the transmitter will operate instantaneously upon the closure of Lswitch 84.

Continued rotation of the camwill open the contacts of switch l84 and deenergize the relays 33 and 24 which willthen resume their normal positions indicated in Figure 3 and the transmission of a wave will cease. Since, as previously l described, the motor ,8i operates at a substantialls7 constant speed, the closure of switch ,contacts Se will be periodic and thus a periodic signal comprising a radio frequency carrier modulated by an audio frequencysignal will automatically be transmitted.

The rate -atiwhich these periodic signals are transmitted is dependent upon the-particular application. As mentioned in connection with the block diagrams of the central station and the mobile station, Figures 1 and 2 respectively, the periodic impulses of the type just described are utilized as a checking signal in order that the operators may have a positive indication that the system is in proper working order.

Since, however,-it is desirable in this novel system to permit the operator of the mobile station liti Y `Since the operation of the power transfer relay 33 is periodic in accordance withV the operation of switch contacts 84, the application of power to the transmitting circuits periodically occurs for a relatively short time. Therefore, since the modulated carrier of the transmitter is only generated for relatively short intervals, considerable economies are effected and the consumption `of electrical energy is greatly decreased.

As hereinabove described, the monitor pilot light 35 shown in Figures 1 and 3 provides a visual indication of the fact that a modulated carrier is being generated. Energy for the operation of the relay controlling the pilot light 35 is derived from inductive coupling with the tank' circuit of the transmitter.- As illustrated in Figure 3, a coil |2| is inductively coupled with the tank coil 93.

The coil |2| is tuned to the carrier lfrequency 'by the variable condenser'l22 and thepotentiall appearing across this tuned circuit is impressed through the parallel combination of grid leak |23 and condenser |24 upon the control grid of -an electron tube |25 which functions in this instance as a grid-leak detector. The anode circuit f of the tube |25 is joined to the source of high potential through load resistor |26 .and the output of this tube is coupled through condenser |21 to -the anodes of a signal rectifier |3I.

The rectified modulating signal energy then Aflows through the coil of the monitor relay 31 to cause the operation of contacts 31 thereof. The contacts 31' are joined in series with the monitor light 35 and this series circuit is connected to a power source suitable for energizing the monitor light 35. l

y In the embodiment illustrated in Figure 3, the monitor light is of a relatively low voltage type and is energized from the filament supply obtained from transformer secondary 14. A con--l denser |32 is connected across the monitor light in order to prevent radio frequency energy, which may be present in the relay leads due vto stray coupling, from being fed back into the'input cir- .cuit by interconnecting cables.

Since the coil of relay 31 is energized bythe Irectified demodulated energy coupled from the .tankcircuit the monitor pilot light will flash, whenever a modulated carrier isgenerated and a signal transmitted. The relay 3`|1wil1 normally tend to follow the variations of the modulations ywhich may, if desired, be smoothed as desired -by a filter circuit to preclude chattering thereof.

1A condenser, |33, is placed across the winding 4of relay 31 to by-pass the alternating current component of the rectified audio frequency signal.

The transmitted pilot light 4| is energized y through the switching members of the power l transfer relay 33 from the lamentsupply of the -transmitter. This light will therefore yoperate whenever plate power is applied to the transmitter circuits and thus during the normal operation of the central station will flash periodically in accordance with the closing of switch 84.

If the central station operator desires to ltrans-- mit a message to the operator of alocomotive in vthe classiiication yard, the switchr32 isclosed.

vrectier |0| to the coil of input transfer relay I-3| and accordingly cause the switching members i4, 3 thereof to move downwardly` and, as indicated, to interrupt the control signal circuit from the tap on power-supply resistor |03 to the input transformer |05, and to complete the circuit from a microphone 26 to this input circuit.

In addition, the switching members of this relay complete a circuit from the high voltage point of rectifier |0| to the parallel coils of relays 33 and 91, provided relay 42 is not energized. These relay coils, when energized as previously described, will apply a high potential to the plate circuits of the various vacuum tubes at the transmitter `and will connect the antenna 23 to the tank circuit of the transmitter. Thus, the transmitter is in a condition whereby speech energy impressed upon microphone 2S is amplifled and caused to modulate the radio frequency carrier in power amplifier 92, the energy from which is then radiated into space through antennal 23.

. Furthermore, the operation of relay 43| in disconnecting the source of constant amplitude audio frequency checking signal from the input circuit of the transmitter precludes interference between speech transmission and the checking impulses despite the continued operation of motor 8| and the continued closure of switch 84.

Therefore, the operator ofthe central control rstation may transmit a message by operating the switch 32 and speaking into microphone 26. Since the receiver at the mobile unit is normally in a position for the reception of energy, the operator of the central station may immediately establish communications with the operator of a mobile unit within the same signaling zone.

The receiver of the central station permits the reception of signals from the classification yard locomotive whenever the engineer thereof desires to call in, check instructions, or acknowledge an instruction. This receiver is normally in a position whereby energy transmitted from the locomotive -station may be received.

The central station receiver illustrated in Figure 4, and in block diagram, Figure 1, is related to the central station transmitter illustrated in Figure 3 in that a common antenna may be employed in both circuits and that power for the operation thereof is sequentially applied in a predetermined periodic signalling cycle as determined by the operation of synchronous motor 8| and associated cam 82.

The power transfer relay 33 illustrated in Figure 3 is common to the receiver and to the transmitter and these are interconnected between the terminals |4|. Furthermore, the common antenna 23 illustrated in Figure 3 is connected to the receiver through antenna transfer relay 24 and through a connection joined to terminals |42|42 at the receiver and transmitter. y

When the power transfer relay 33 andthe antenna transfer relay 24 are in the position indicated in Figure 3, the receiving circuits are energized and the antenna 23 is joined to the input circuits and thus places the receiver in a condition for the reception of signals intercepted .by the antenna. The receiver may be energized from an individual rectifying circuit energized from the same source of alternating current and impressed upon the receiver terminals |43.

The lplate transformer |44 and the filament transformer-.|41 are continuously energized from the terminating current source |13.v Conventional filter section |46 is joined to the filament of the rectifier |45 for eliminating the ripple o f theI yrectified potential, A bleeder resister |48 `is` shunted across'the output offthefltersection Hit. The high potential lead for energizing. the

plate circuits of the various electron: tubes is broken-at mi by means of normally closed conitacts 33" on' the power transfer relay" 33` as in'- dicated in Figure 3. The interconnection of Figures 3 and 4 is shown by the corresponding terminals |4| on both figures.

The filaments (not shown) of the electron tubes indicated in Figure 4 are all continuously energized from the power transformer secondary |41 and thus, as shown, in Figure 4, power is applied to both anode vand heater circuits of the receiver.

Incoming signals intercepted by the antenna 23 are impressed upon a radio frequency transformer |5ithe secondary of which is tuned by a variable condenser 52. A radio frequency amplifier |53 of 'conventional form is utilized to raise the level of incoming signals and the output thereof is coupled through condenser |54 to agrid ofconverterv tube |55.

A- beat frequency oscillator tube |56 utilizing a crystal |51 for frequency control generates a continuous oscillation which is coupled from coil |B| to another grid of the converter rtube |55. This radio receiving circuit may comprisethe conventional superheterodyne circuit for receivingand demodulating incoming signals. Thus, the Voutput ofthe converter tube'l55 is coupled through an intermediate frequency transformer |62 to the control grid of an amplifier |63.

The output of this last mentioned amplifier |63 is then coupled through the intermedia-te frequency transformer |64 to a second amplifier tube |65. This tube has a diode section energized through condenser |61 and having a'load resistor |68 which furnishes a/negative biased voltage for automatic volume control as is well known in the art. The output of the amplifier tube Hit is also coupled'to intermediate frequency transformer l to one anode |19 of the double diode rectifier tube l| |56. The variable potentiometer |1| acts as a diode load and is coupled through condenser |12t0 the grid 'iE-'3 ofthe dual triode |8|.

The diode load |1| is by-passed by condenser |11?r which acts as a radio frequency filter. This diode load 11| is'also shunted by the otherr diode section of tube |56, and condenser |15. This acts as a noise discriminating and limiting circuit. The arm of the potentiometer |1| is connected to grid |16 of the dual triode tube |8| through the filter resistor |11. When no carrier is present the grid |16 is at zero potential with respect to its f associated cathode and therefore the effective plate resistance is very low. By means of the voltage dividing network comprising resistors IEE and |83, the grid 513 through its gridleak |19 is maintained at a high negative voltage with respect to its associated cathode. This high negative b-ias effectively reduces the amplification of the tube to a minute value and causes a cessation inthe flow of plate current. When a carrier is present and amplified by the respective radio frequency and intermediate radio frequency amplifiers and rectified by means of the diode |56, a negative voltage appears across potentiometer I1 This voltage when applied from the adjustable arm of the aforementioned potentiometer to thelter `resistor |11 through the grid |18 of the dual triode |8| causes the plate resistance Athereof to increase considerably in value. This by means of the aforementioned voltage dividing network causes the grid |13 to assume its normal CTI i6 operating bias with respect to itsy associated cathode. Thus, audio-frequency noise suppressionv is effected, under'con'trol of. an `incoming radiofrequency carrier.

Therefore, plate current will flow through |82 and thru the relay 42 causing the switching members to operate; Since the winding of the relay 42 has a' high impedance to audio-frequencies, this winding` together with the ccmp'en'satirrg.` resistor |92 acts as the plate load for |32' `and thus the audio-frequency signals are coupled by means of condenser |83 and volume control ivtl'toV the input grid of the power amplifier tube |85.

The outputV of amplifier' |35 is coupled through transformer |81' inthe `anode circuit thereof to the' loud speaker 25 'and to a plug |3| whereat earphones may be connected if desired.

The anode |82 is energized from the high. positive potential through a parallel combination of load 'resistor' |92 and the coil of suppressor relay 42. An incoming carrier intercepted by the antenna 23 and amplified and demodulated in the various receiver circuits illustrated in Figure 4 will thus cause the energization of the coil of relay42- to cause'the movement of switch members This novel manner of actuating a lock-outl relay 42 inserted in an audio-frequency noise suppression circuit in accordance with an incoming radiorfreduency carrier is illustrated in both Figures 3 and 4 and the various connections of the switching members are best illustrated in Figure 3. Thus it may be Yseen that the energization of the coil of relay 42 due to a received signal will cause the movement of the switch members to open the series circuitv of switch 84 and contacts 8 between the coils of relays 33 and 24.

Accordingly, the continued operation of the switch 84 under the influence of the cam B2 will have no effect upon these circuits. The operation of the switch members of suppressor-actuated relay 42 also completes a circuit from the filament winding 14 of the power transformer to the call light 43 and thus when a signal is received, the calling'light will flash. An incoming signal will operate lock-out relay 42 as previously described to preclude the operation of power transfer relay 33 and antenna transfer relay 24 from the positions indicated in Figure 3.

Therefore, the reception of a signal will pre- 'clude the transmission from the central station vof the checking impulse or speech transmission which would normally tend to interfere with the signalreceived.v As the vantenna 23 is alternately switched from the receiver circuit to the transmitter circuit, reception will only take place when in the position shown in Figure 3. This permits the operator of a classification yard locomotive, by themere transmission of his carrier wave, to maintain the central station in condition for receiving the signals.

The engineer may transmit speech signals from hisvehicle transmitter which will be made audible through the agency of the central station loudspeaker 25.V Or he may by merely keying his carrier in accordance with a predetermined code, cause the calling light 43 to flash correspondingly.

When the operator of the mobile unit deener- 'gizes his transmitter, the lock-out relay 42 automatically is deenergized and permits the switching-member 42 toras'sume the position indicated in Figure 3, which thus permits keying of the central Station carrier Wave in accordance with the .to be described in connection with Figures 'v7l and 17 checking signals generated by the cam 82 and the switch 84, and speech transmission initiated by foot switch 32.

The modification of the central station circuit described in connection With Figures 3 and 4 utilizes a single antenna for the transmission and reception of signals.

It is pointed out that various known forms of transmission systems may be utilized in connection with a classification yard traffic coordination system of the nature being described. Thus the receiver and transmitter units at both the central station and the mobile station within a locomotive may be of the ultra high frequency type employing directional radiation or non-directionalv radiations. 1

'This of course constitutes no limitations whatsoever since the various longer wave transmission systems may be utilized, if convenient.' This ywill merely necessitate a modification of the modulators and amplifiers. Furthermore, the common antenna illustrated may-be dispensed with and an individual antenna employed for the receiver circuit and the transmitter circuit. i

If a separate antenna is employed it will eliminate the need for antenna transfer relay 24 and the circuit connections which are vnecessary Vto cause the proper energization thereof vas described. i

. However, with an ultra-high frequency system of the illustrative typedescribed herein, a single communications channel may be employed for both transmitter and receiver. This is preferable in the illustrative case,.since it .permits the employment of a single tunedantennacircuit of l high efficiency for both units.

On the other hand, adistinct carrier frequency may be utilized for each station. and the lcircuits necessary for demodulation and transmission may be varied accordingly as is well known in the art. It is also possible with thegeneral system dis-1v closed in connection with the central station unit illustrated in Figures 3 and 4 to utilize the. technique of localized traffic lane signalling within a restricted locality disclosed in copending application Serial No. 260,644, filedMarch 8,1939, now Patent No. 2,255,055; issued September 9, 1941.

As disclosed in copending application Serial No. 260,644, electric wave signalling may be effected in a localized area along a trafiic lane by means of a transmission cable disposed Within-fthe area for the extent of a signalling zone.

Y The mobile unit to be described in connection with block diagram Figure 2 and subsequently 8, may of course utilizeany of the aforementioned signalling channels. The receivingk circuit illustrated in Figures'? and 8 correspondswith the .-diagrammatically illustrated mobile receiver of Figure 2 and similar reference Vriu"1r1era.ls will be carried over to designate similar' elements.

This mobile station may, if used upon the classi- 'fication yard locomotive, be most conveniently ing conditions the receiver `is continually e'nergized and the antenna is joined thereto in order ythat any signal transmitted. from .the central station be immediatelyapparent within .the loco- -motive cabs.

Thus, as shown, through antenna trans-fer relay i 155,'v the antenna 5| is coupled to the input radio frequency transformer 20| of the receiving circuit. The receiver is substantially similar to that utilized at the central station and illustrated in Figure` 4.

The power required for driving the various transmitting and receiving circuits illustrated in Figures 7 and 8 is obtained from a. locomotive electrical power supply which is a conventional 32 volt direct current supply. This supply is utilized to continuously energize all of the laments of the combined circuit in accordance with circuit 202.

The variable resistor 203 is inserted in series with the filament circuit 202 and the direct current impressed upon terminals 204. To obtain the required voltage for driving the plate circuits of the various tubes, a small motor generator, employing a motor unit 205 is utilized to drive a directly-coupled generator 206 to generate the required voltage.

This voltage is filtered by the circuit of chokes and condensers 201 t0 remove any commutator ripple or the like. The output high direct-current potential is then selectively impressed upon the plate circuits of the receiver or the plate circuits of the transmitter as determined by the position of power transfer relay 64 which operates simultaneously with the antenna transfer relay 55. As shown, the high-direct-current potential is coupled to the anode circuits of the receiver electron tubes and the antenna 5| is coupled to the input transformer 20|. Y

The receiver comprises essentially a radio frequency amplifier 2|| energized by the potential developed within the tuned radio frequency input circuit 20|. The anode of this radio frequency amplifier is energized from the high potential generated by the motor generator 205, 206 and the output thereof is coupled through circuit 2|2 to one grid of a converter tube 2|3.

A heterodyne oscillator 2|4 utilizes a tuned circuit 2|5 and a crystal 2|6 for determining the frequency thereof and the continuous frequency output thereof is impressed through coupling condenser 2 |i upon another grid of the converter 2|3.

The beat frequency component of the output of converter 2|3 is selected and coupled to the intermediate frequency amplifier 22| by anv intermediate frequency transformer 222. This amplifier operates in conventional manner and the output thereof is coupled through intermediate frequency transformer 223 to` the input of the diode-pentode tube 224 which in turn is coupled to the automatic volume control circuit and a demodulator and noise limiter as hereinabove described in connection Vwith the central station receiver illustrated in Figure 4.

The demodulated output of .this receiving circuit is then coupled to a double triode electron tube 226one section of which functions to amplfy the audio-signal. The other section of tube 226 acts as a suppressor circuit as described in connection .with the similar circuit of Figure 4.

The signal is then coupled through condenser 231 to a power amplifier 24| the output of which is coupled through transformer 242 to an ear- .phone connection 243 and a parallel two-channel v.filter (illustrated in Figure 8) through the termi- -nals 3 and 4 of the Yconnector 244 illustratedl in 1both Figures '7 and 8.

Referring now to Figure 8, the iilter section comprises essentially a parallel arrangement wof high pass and low pass filter sections ljoined to 19 the terminals 3k and li of the connector 244. Thus a W pass filter which may in one form comprise series chokes 245 and shunt condenser 24d will effectively block the passage of high frequency signals While permitting the unimpeded passage of low' frequency signals therethrough.

The. high pass filter in. parallel, with the low passlter section4 joined to. terminals 3 and a of connector 344 comprises essentially a plurality of series condensers 24'! and shunt inductance 25E. This filter section then will preclude the passage of relativelovv frequencies while permitting the unimpeded passage of the higher frequency signais. rIhe design of the filter will determine the extent to which attenuation or signals of various frequencies may be effected. Hence the high pass filter section may be designed to pass a relatively small amount of low frequency energy-to permit limited aural reception of ther checking signal,I if

desired.

Accordingly, demodulated energy applied to the terminals 3 and i from the output of thev power amplier 24E will selectively pass through filter circuits depending upon the nature oi' the signal. lf thereceived signal comprises the low frequency checking impulses periodically transmitted from the central station in the manner described in connection with Figures l, 3 and 4, then the low pass lter section will permit the passage of the demodulated currents which will then be. impressed upon full wave rectiying unit 252.

This rectifier, may comprise a small dry-disc bridge as indicated, and the low frequency checkn ing signal will be rectied therein and as illustrated, the output thereof is impressed upon the coil 253 of the checking signal relay 62 illustrated also in Figure 2.

Since the current is or a fluctuating nature, although rectied, a condenser 254 is shunted across the relay coil to preclude chattering and improper operation of the relay coil 253. Thus it may be noted that the checking signal transmitted from the central station periodically due to the operation of synchronous motor Si and correspondingly switch 84 will` be received at the locomotive inthe classification yard and will be demoolulated and amplied and impressed upon a relay 82.

The switching member 62' of, this relay will therefore operate in a manner which corresponds with the operation of switch lili during normal operation of the two-way signalling system. The closure of relay S2 as indicated in Figure 8 will short-circuit a section of a variable resistor 2M. This resistor 2st is joined in series through terminals and 2 of connector 44 indicated in Figures '7 and 8, with a checking pilot light (i3 and the entireseries circuit is connected between the direct current supply of the locomotive and ground.

Therefore, the checking pilot light 63 is continuously energized by the passage of current therethrough, this current being determined by the magnitude of resistor 26|.

Upon the receipt of a checking signal, the contacts of checking relay t2 are closed and a section of the resistor Ztl is short-circuited asdetermined by the position of the variable tap 2F33. Therefore, the checking light will ilash to full brightness upon the receipt of a checking impulse and indicate in the manner described, the proper operation of the transmitting and receiving circuits. The output of the high pass lter comprisingv the condensers 2M and the choke 25| is coupled through transformer 264 to the loud speaker 51. Y

A received speech transmission will "pass through the high pass filter section and energize the loud speaker and so permit the central station operator to instruct the operator of the classication engine. The speech transmission will not effectively ow through the low pass lter and thus will not energize the checking lamp.

The checking signals may, as described above, be permitted to energize theloud speaker 5l to provide an audible check on the operation oi the traic communication system. Thus the checkn ing signals will periodically cause the flashing of the lamp and simultaneously cause a distinctive checking or proceed tone to be heard from the loud speaker. y

Since the checking signals are automatically cut out at the central station, as described, when speech is being transmitted, the checking signals vwill not interfere audibly with this speech. The

locomotive engineer is provided, by the apparatus illustratedfin Figures: 7 and 8, witl'ir a transmitter for. calling and speaking to the central station operator. The filaments of this transmitter are normally energized from the locomotive 32 volt supply. The plate circuits thereof are normally deenergized and the antenna 5I is normally uncoupled therefrom.

When the engineer desires to call the central station, he may depress his transmitter switch 5d which, as illustrated in Figure 7, joins coil 2li of relay 272 between the direct current source availn able and ground. A resistor 2l3 reduces the flow of current in the relay winding to prevent damage tothe relay coil 21|. 1

In addition, the operation of switch 5L? energizes the coil 274 of the antenna transfer and power transfer relays 55 and respectively, and

' thus causes the consequent movement of the 'switch arms which in turn Aconnects the antenna 5| to the output of the transmitting circuits and applies the high potential available from the generator 206 to the transmitting anode circuits and disconnects this potential from the receiver cir'- cuits.

The energization of relay coil 2licauses the movement of the switching members 2li downwardly` as viewed in Figure '7 to close their respective circuits and as indicated, complete one circuit from the positive terminal of the direct current available at the terminals 2de through the switching member and through a variable resistor 216 to ground.

The variable tap of the resistor 2id then is joined in circuit through the primary of the transmitter input transformer 2'55, through the microphone 65 to ground. Thu-s an energizing potential' is impressed upon the microphone 65 `which is preferably of the carbon type since relatively high gain is obtained immediately at the microphone. Y

The otherswitching member of the relay 272 short circuits asection of a variable resistor 28| Thisresistor is in series with a transmitting pilot light 6 and thev series combination is joined to the terminals 264. The resistance in the transmitting pilotlight circuit presented by resistor 281 is normally suiiiciently great to precluderthe illumination of transmitting pilot bulb 5E.

However, upon theoperation. of relay 272 and the short circuiting of a section of the resistor 28|, the lamp 66 glows to indicate that the transmitter is being energized'. The transmitter may -be of any conventional form and, as illustrated,

'essentially comprises, an. oscillator '282.` having a ingthe frequency'thereof." Y

^ The ioutput of theoscillatoris coupled to the control grid of a power amplifier 285, the plate circuit of which' is energized from the high potential source through inductance 286 and through radio frequency choke 281 and tank in- The screen grid' ofthe :power amplifier 285 is also energized fromthe highpotential source through inductance 286 and through resistor 292. t t,

Sound waves. when impressed upon .the carbon microphone 65 establish corresponding electrical fluctuations which. are. vimpressed upon the. primary'oftran'sformer 215 and cause corresponding electrical variations in the secondary thereof which is joined to the control grid of modulator tube 295. Y

The screen grid of the modulator-295isfjoined to the high potential source and the plate circuit thereof is Ajoined, thereto'through the inductance 286. The amplified signals which appear in the Voutput circuit of the modulator 295 modulate the radio frequency-carrier generated bythe oscillator 282 land its associated crystal 284.

Thugs when speechisimpressed upon the microphoney B5 andthe switch 5I isclosed, the antenna v5|l will radiate a carrier `modulated in accordancewith the speech.V If no yspeech is impressed upon fthe microphone, the carrier only-Will be radiated. lThe radiated signals will be received at the receiver illustratedinFigure 4 at. the centralstation kand in the time intervening between two vsuccessive checking impulses, ythe radiated carrier ormodulatedcarrier will f. cause the suppressor relay |18.Y ofy the central station to operate tonpreclude the.. further Vtransmission of checking signals. f Y

`Thistraiiic communication system may beeinployed 'WhereverVV mobile units `are operated. in a s 'localized .signalling area. Where applied to. railroadwork and more specifically to classiiication ,indicatingilights into .a single compact vunit as'illustrated in Figures 5. and 46. The loudspeaker is mounted withinahousing 38| in a position slightly above ear-levelwheresounds may most easily be detected...A flexible or non-flexible arm 302 supports the" microphone 28 within a yhousing 303 attachedto'thefarm at 304; y l -In addition, the housing alsok provides supporting means for the three indicating lights at the central station schematically illustrated in Figure 1 and in the circuit diagrams of Figure 3. These lights may be of a distinctive color and are energized through the necessary wiring indicated in Figure 3, this wiring being carried through the flexible arm 302.

The entire assembly of microphone, loud speaker and checking lights may be disposed at a central control point within the station which, in turn, may be located adjacent the hump of the classification yard.

If the operator is in an elevated position, with respect to the hump, in a control tower, then the microphone and loud speaker assembly indicated in Figures 5 and 6 may be disposed adjacent a window overlooking the yard. The foot switch 32 which, when depressed, permits the transmisv.sion of speech from the central station, may be disposed Adirectly beneath the combined microphone and loud speaker assembly.

The central station operator .will always have the microphone available forspeech transmission and, by merely depressing the foot switch, may call a locomotivewithin` the classiiication yard and relay the required instructions. Furthermore, at all timesI the three indicating lights',` Il, 43 and 35 will be in his field of vision in orv'der'that he may'ascertain theY correct operation ofthe system.

Since vthe operator i indicated in Figures 9,V` 10 and 11, the microphone ofthemobile'unit may be of similar con- Y struction.

VThus the microphone'85 is supported upon a flexible 'arm 3|| which in turnis carried upon a support 3|2 which may be secured to theroof lof the locomotive, or other vehicles, bya plurality of -screws 3|3.

The microphone-inthis embodiment -is mounted within a shock resistanthousing in order that the-vibration andf the llike experienced vby the locomotive will not injure the sensitive microphone 'nor cause undue transmission of noise. Thus, asv indicated in- Figure 10, the microphone 65V issupported substantiallyv centrally within a housing3|4-which isjoined to the lflexible-arm The flexible arm carries thenecessary microphone Wires 3 I 5 therethrough to permit the energiz'ationthereof and thetransmission of speech currents. The relatively large space between the microphone and the-outer Wall of the supporting housing 3|4 is packed with a highly-resilient material 3|6 or the like in order that the jarringof the housing will beeffectively damped and not transmitted toV the microphone itself.

AThe indicating lights 63 and 66 at the transmitter, -which visually indicate the checking signal and show that the locomotive transmitter is not in operation, maybe mounted upon the mithe interior 'of `a locomotivecab. i

i The engineer. as is well known, normally must observe vthe'roadway in performing the various ,operations andjcannot conveniently employ his hands to'hold a microphone. Thus, we prefer to suspend the microphone directly within the engineers field of vision by means of the fiexible arm 3| by securing the support 3|2 to the roof of the cab, and extending the flexible connector so that it projects inward with respect to the windowr32| of the locomotive.

The directional loud speaker 51 employed within the locomotive cab may be disposed behind the engineers seat 322 and directed towards him so that the speech signals will readily be audible. Accordingly, the engineer will receive transmitted speech signals by loud speaker 51 and will at all timues have the checking signal in his field of vision to ascertain the proper Working order of the complete communication system.

The transmitting switch 54 may be disposed adjacent the sash of the window 32| in order that the engineer may conveniently operate this y switch without moving from his normal posiwill always be near the microphone and loud speaker assembly, the call- 23 he will atV v,all times be able to observe pperation -of the check-ing or proceed signal :and transmitting pilot light indicators.

While there v.has been described what is at present considered `the .preferred 'embodiment kof the invention, -it Willbe obvious to those .skilled inthe fart that various 'changes and A1modic'ations may be made therein without Ideparting :from the invention, and it is, therefore, aimed in the appended claims to cover all such changes @and ,s

-modications as fall Within `the true spirit `and scope o'f `the invention. l

I claim:

1. In asignaling system of the type described,

a transmitter adapted to be under selective -control of -a'n operator and receiver, 'a rel'ay transferring `,power alternatively to said transmitter and said 4receiver during the interval when said transmitter-fis-not under control of said` -operator, periodic means for energizing said relay, and a monitoring .signal yactuated by the movement of said relay so yas to vindicate when 1power is transferred to said transmitter. y

2. In a signaling system of the type described, -an antenna and arreceiver, shifting means periodically connecting saidreceiver to said antenna, a noise suppression circuit in said receiver yielding `a sharp `discrimination between -signals below and above a predetermined. energy level, and a relay connected to said noise suppression circuit and acting, upon the passage ci signals through said noise suppression circuit, tosuspend the operation vof said v.periodic shifting means, whereby said receiver remains connected to said antenna during ysignal reception.

3. In a signaling system for effecting automatic supervisory signaling fbetween aV central station and Ia remote unit, wherein the central station includes va iirst carrier wave ltrar-isrnitter, carrier waveV -receiving -means responsive to carrier wave energy from said `remote unit, and wherein said remote vunit Iincludes carrier wave receiving means responsive to carrier wave energy from said lcentral station, and .a second carrier wave transmitter, fthe combination .which comprises, a source of audioV Afrequency control signal energy at said central station, yautomatic switch-ing -means Vfor `periodically effecting emission of a carrier wave by said central station transmitter and concurrently impressing said signal energy on said carrier Wave, and a visual indicator disposed at said central station, a lockout relay connected to the carrier Wave receiving means of said central station, 'and responsive to 'cluding 'a noise 'suppression circuit and said lockout relay being connected to said lnoise suppres- `sion circuit, whereby `the operation of said :relay is .positvelydetermined by the reception Yof a signal above a predetermined `energy level.

WILLIAM S. HALSTEAD.

vREFERENcEs @Ceran The following references are of record Jiin the file of this patent:

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